1. Field of the Invention
The present invention relates to a gas fuel injection control device of an internal combustion engine for vehicle, and more specifically to a gas fuel injection control device of an engine for vehicle in which the accuracy of a calculating method of an intake pipe internal pressure for use in an injection quantity control of a gas fuel in a constant-speed operation and transition operation states such as acceleration and deceleration operation states of the engine.
2. Description of the Related Art
A gas fuel injection control device of an engine for vehicle that is supplied with a gas fuel such as CNG (compressed natural gas) reduces the pressure of the gas fuel supplied from a fuel container using a regulator and injects the gas fuel, which has been reduced in pressure to a set pressure, from a fuel injection valve. The regulator operates so that the intake pipe internal pressure introduced from a surge tank part of an intake manifold via a hose and the gas pressure upstream of the fuel injection valve are constant. The gas fuel injection control device detects the intake pipe internal pressure and the gas pressure upstream of the fuel injection valve and controls the fuel injection time according to a pressure correction coefficient that is inversely proportional to the differential pressure between them.    [Patent Document 1] Japanese Laid-open Patent Publication No. 7-189811    [Patent Document 2] Japanese Laid-open Patent Publication No. 62-13766
Incidentally, the gas fuel injection control device of an engine for vehicle in the related art performs the same filtering in the processing of the intake pipe internal pressure value irrespective of the engine in the constant-speed operation state or in the transition operation state, and therefore has following problems.
One of the problems is that, in the constant-speed operation, there is not a large difference between the differential pressure detected by the gas fuel injection control device between the intake pipe internal pressure and the gas pressure upstream of the fuel injection valve and the differential pressure in the regulator, whereas at the abrupt acceleration operation or the abrupt deceleration operation, a difference occurs between the differential pressure detected by the gas fuel injection control device and the differential pressure in the regulator because of a response delay of the regulator, resulting in failure to appropriately calculate the pressure correction coefficient.
Performing the filtering of the intake pipe internal pressure in consideration of the response delay of the regulator at the transition operation as measures causes another problem of failing to detect the pulsation of the intake pipe internal pressure and the gas pressure at the constant-speed operation, resulting in failure to appropriately calculate the pressure correction coefficient.
Another problem is that because the same filtering is performed at the constant-speed operation and the transition operation, it is impossible to appropriately correct either the pressure correction at the constant-speed operation or the pressure correction at the transition operation, causing excess or deficiency of the fuel injection quantity and affecting the operation of the engine.